An apparatus device for removing material from a liquid flowing through a channel is known from German Patent No. DE 34 20 157 C1 corresponding to U.S. Pat. No. 4,634,524. The known apparatus includes a cylindrical sieve grate which is partially submerged in the liquid with its axis in inclined manner, the grate having a hydraulically open front side on the inflow side thereof and a hydraulically substantially closed back side on the outflow side thereof. The sieve grate includes a perforation of slits forming a separation surface on the inner side, while the liquid penetrates the slits and remains in the channel. The cylindrical sieve grate is rotatably driven in connection with a screw conveyor. The screw conveyor has a feeding hopper being coaxially arranged in bearings with respect to the sieve grate. The screw conveyor includes a housing and a conveying screw. A fixed detaching device in form of a brush roll or a spray rail for water for detaching the material to be raked and/or screened adhering to the separation surface inside the sieve grate is provided on the outer side of the sieve grate, above the feeding hopper. The rakings fall in the feeding hopper being the first element of the screw conveyor, and they are upwardly conveyed to the discharge point outside of and above the liquid. The cylindrical sieve grate includes spiral guide plates arranged on the inner side of the grate having the function to convey upwardly especially larger rakings and to hinder them from falling back during rotation of the sieve grate. The openings of the perforation of the sieve grate may be designed to have a size of between several millimeters to about 10 mm. Smaller openings cannot be produced economically. Consequently, the known apparatus cannot be used to treat sludge-like screenings.
An apparatus for removing material to be raked and/or to be screened from a liquid flowing in a channel is known from German Patent No. DE 36 30 755 C2 corresponding to U.S. Pat. No. 4,836,919. The known apparatus includes a driven cylindrical sieve grate being positioned in inclined manner in the channel. A screw conveyor leads from a feeding hopper being arranged near the sieve grate to a discharge point outside the channel. The sieve grate includes a number of ring-like discs being arranged side by side with distance to each other in order to form slits. A stripper bar forming a detaching device is positioned inside the sieve grate above the feeding hopper. The feeding hopper includes a wall upwardly extending to the stripper bar. The stripper bar may be positioned on the outside of the sieve grate also extending inwardly through the slits between the ring-like discs. There are constructive limits in the design due to the formation of the openings of the sieve grate in form of the number of ring-like discs. Consequently, the known apparatus can be used to remove rakings rather than screenings. Sludge cannot be screened using the known apparatus.